1. Field of the Invention
This invention relates, generally, to systems and methods for treatment of wastewater and, more particularly, to systems and methods for continuous treatment of influent wastewater in a single tank.
2. Prior Art
Numerous devices are known in the art for the treatment of wastewater. Most treatment systems have at least two separate tanks: a treatment tank for aeration of the wastewater, and a settling tank for removing bio-solids. An inlet in communication with the treatment tank, an outlet in communication with the settling tank, and a conduit in communication with the treatment tank and the settling tank are normally provided in the wastewater systems. Influent is fed to the treatment tank via the inlet and treated wastewater is removed from the treatment system via the outlet.
In the treatment tank, oxygen is typically provided to the microbes to aerobically oxidize the organic pollutants in the wastewater. Typically, air may be injected into the treatment tank at various locations via an aeration source, such as an aerator, so that a sufficient amount of oxygen is transferred and distributed throughout the treatment tank to support the aerobic bio-activity. Typically, the aerator is a conventional design, such as, for example, a fine bubble diffuser, a coarse bubble diffuser, a jet aerator, an inductor aerator, a low speed mechanical aerator, a high speed aerator, and the like. The treatment tank tends to be a fairly high energy environment to keep microbial solids suspended (i.e., mixed) and to supply the mixture with the appropriate level of oxygen.
The aerobically treated wastewater is generally delivered to the settling tank via at least one conduit extending therebetween. Typically, a gravity flow conduit or a pressurized conduit delivers the aerobically treated wastewater to the settling tank. To allow the bio-solids present in the wastewater to settle, the settling tank typically is designed as a generally low energy, quiescent, environment. Treated wastewater is removed from the settling tank through the outlet.
As noted above, the general state of the art is to employ a separate tank for each sequential phase of the treatment cycle. That is, to use at least one treatment tank for aerobic bio-treatment, and to use at least one settling tank for settling of bio-solids. The disadvantages to the use of separate tanks include the greater use of land and the additional cost of building two tanks and the plumbing to connect the two tanks. Various designs of single tank wastewater treatment systems have been proposed to overcome the noted disadvantages.
One common type of a single tank wastewater treatment system incorporates both a clarifier chamber and treatment chamber into a single tank. A partition is typically provided within the tank to create the two chambers, a lower aeration chamber and an upper clarification chamber. The partition does not extend to the floor of the tank and defines an opening so that the two chambers can be in fluid communication. Examples of such wastewater treatment systems are shown in U.S. Pat. No. 6,096,203 to Drewery, U.S. Pat. No. 5,785,854 to McKinney, U.S. Pat. No. 5,549,818 to McGrew, U.S. Pat. No. 5,490,935 to Guy, U.S. Pat. No. 5,221,470 to McKinney, and U.S. Pat. No. 4,983,285 to Nolen. The wastewater treatment systems described in the exemplary patents can adequately be characterized as aerated septic tanks and are generally small, with a capacity typically less than 2500 gallons. Such aerated septic tank systems are suitable for only very low volumes of wastewater, with flow rates ranging from only 500 to 1,500 gallons per day.
An alternative example of a single tank wastewater system is demonstrated in sequencing batch reactor (SBR) wastewater treatment systems. SBR wastewater treatment systems typically use only one tank in which aeration and clarification are achieved by alternatively aerating a batch of wastewater in the tank, during a reaction phase, then turning off the aerator to allow the bio-solids to settle, in a clarifying phase, so that clear, treated effluent forms above the bio-sludge blanket formed by the settled bio-solids. During the clarifying phase no liquids enter or leave the tank to avoid the introduction of turbulence in the supernatant. After settling, in a decanting phase, treated effluent is withdrawn from below the surface of the mixed liquor to avoid disturbing the settled bio-sludge. The tank is then refilled and the reaction phase is reinitiated. By definition, SBRs process intermittently so they are only suitable for very low volumes of wastewater. To overcome the low volume limitation, SBRs often use two tanks so that one tank is being aerated while the other is settling. To function properly, SBRs require the use of programmed timers and pumps to properly control the sequential processes that take place in the single tank, and, if used, to alternate the processes between the two tanks.
The present invention overcomes the prior art limitations by providing a system and method which is highly reliable, relatively economical in manufacture, cost effective in installation, and allows for relatively high flow rates of treated wastewater.
In one exemplary embodiment, the wastewater treatment system includes a treatment tank having an internal partition, a wastewater inlet line, an effluent discharge outlet line, and an aeration source. The partition is connected to a side wall of the tank intermediate the bottom and the top of the treatment tank and divides the tank into an upper aeration chamber and a lower clarification chamber. The partition defines an opening that is spaced from the bottom of the treatment tank which allows for fluid communication between the upper aeration chamber and the lower clarification chamber. In one example, the partition may have, in portion, an inverted frustoconical shape.
The wastewater inlet line opens into and is in fluid communication with the aeration chamber of the treatment tank. The effluent discharge outlet line is in fluid communication with the clarification chamber for communication of treated wastewater away from the treatment tank. The aeration source is positioned within the aeration chamber to supply oxygen to the wastewater in the aeration chamber. The aeration source in the aeration chamber provides mixing of the wastewater within the aeration chamber and supplies oxygen to the mixed liquor in the aeration chamber for efficient removal of organic pollutants.
The treatment tank may also include a second partition that is connected to portions of the side wall of the treatment tank. In position, a top edge of the second partition is proximate the peripheral edge of the treatment tank and a bottom edge is spaced from an upper surface of the partition that divides the treatment tank into the upper aeration chamber and the lower clarification chamber. The second partition forms a separate anoxic chamber within the aeration chamber of the treatment tank. In one example, the wastewater inlet line opens into the anoxic chamber of the treatment tank. The tank may also include a bio-sludge recirculation conduit in communication with a bio-sludge outlet in the bottom of the treatment tank and in communication with the anoxic chamber for supplying bio-sludge from the clarification chamber to the anoxic chamber of the tank.